1. The Field of the Invention
The present invention relates to systems and methods for curing fluids. More particularly, the present invention relates to systems and methods for pre-curing ink before the ink is fully cured.
2. Background and Relevant Art
Many different substances, such as inks, lacquers, and glues, are cured using radiation such as ultraviolet (UV) light. These substances typically contain photo initiators that are activated upon exposure to UV light. When the photo initiators within a substance are activated, the substance cures or hardens. UV cured inks are used in a variety of different printing and non-printing applications. One of the advantages of using UV cured inks is that they are less expensive than other types of ink in part because less energy is required to cure UV inks. Also, inks that are cured using UV light are more xe2x80x9cenvironmentally friendlyxe2x80x9d because they do not contain solvents.
In many printing systems, however, more than one color of ink is used to create an image, with the ink typically placed on a media one color or layer at a time. Because wet ink has a propensity to run on the media and because ink droplets tend to merge together, each layer of ink is usually cured immediately after it is placed or printed on the media. In other words, the first layer or color of ink is therefore cured before the second layer or color of ink is placed on the media. When there are, for example, four different colors of UV ink, there are effectively four layers of cured ink.
FIG. 1A is used to discuss some of the problems that arise when each layer or color of ink is cured separately and illustrates an example of UV inks that are printed in layers. In this example, the different colors of UV ink are printed or placed on a media 100 by different print heads. Each print head is printing a different color of ink on a different portion of media 100. Thus, strips or rows of different colored ink are placed at the same time by the print heads of the printing system, with each row of ink usually cured at the same time. More particularly, the UV inks 114, 116, 118, and 120 are placed at the same time even though inks 114, 116, 118, and 120 correspond to different colors.
As previously stated, ink 114 is placed at the same time as inks 116, 118, and 120. However, ink 114 is in layer 102, ink 116 is in a layer 103, ink 118 is in a layer 104, and ink 120 is in a layer 105. The inks 116, 118, and 120 are printed on other rows or layers of ink that have already been cured. Thus, ink layer 105 is effectively printed on ink layer 104, ink layer 104 is effectively printed on ink layer 103, and ink layer 103 is printed on the layer 102.
While printing one layer of ink on another layer of ink is commonly practiced, the problem of printing UV cured ink on top of another ink layer is becoming evident. Those ink layers deposited last obscure all other ink layer deposited upon the media. Further, because each layer of ink is cured before another layer is deposited thereupon, the layers of ink do not have an opportunity to blend appropriately. These consequences combine to reduce the overall quality of the image being printed. As shown by blocks 112, 110, 108, and 106, the problem becomes more pronounced as additional layers of ink are placed on media 100.
Waiting until all of the ink layers are placed on the media before curing the ink may also lead to unsatisfactory results. In this instance, the inks retain their liquid nature and are prone to losing their place on the media where they were originally placed. This can occur when two droplets of ink are attracted to each other and merge to form a single larger droplet of ink. Wet inks may also run on the media and thus lessen the quality of the image. In these cases, the print quality is again reduced because the inks do not maintain their original placement on the media.
These and other limitations are overcome by the present invention which relates to systems and methods for curing ink by pre-curing the ink first. When UV ink is exposed to UV radiation, the photo initiators in the ink are activated and the UV ink cures or hardens. The UV radiation is often directed to the UV ink using an illuminator that includes a reflector that reflects UV light from a UV source to the UV inks. As the illuminator moves over the printed UV inks, the photo initiators are activated and the UV inks are cured.
In one embodiment of the present invention, the illuminator includes a pair of reflectors: a pre-cure reflector and a cure reflector. The pre-cure reflector is positioned differently within the illuminator than the cure reflector. A pre-cure reflector does not reflect sufficient radiation to fully cure the UV inks. Instead, the pre-cure reflector reflects enough UV light to change the viscosity of the UV inks such that the UV inks do not run on the media. The pre-cure reflector thus cures the ink enough to prevent the ink from running or merging with other ink, but does not prevent the ink from being fully cured at a later time. The pre-cure reflector also ensures that one color of ink is not cured on top of another color of ink. By pre-curing the inks, all of the inks can be placed on the media and create a more uniform surface, whereas curing each layer or color of ink independently often results in a stack of ink layers without a slight blending and more uniform surface. After all of the different colors of inks have been printed on the media and pre-cured, then the cure reflector fully activates the photo initiators and cures the UV inks in a single layer or film of ink.
In another example, part of the illuminator is blocked. The effect of blocking part of the illuminator is that less UV radiation or light is directed to the UV inks and the UV inks are pre-cured. The unshaded or unblocked portion of the illuminator fully cures the UV inks. In another example, a lens or glass plate is attached to a bottom of the illuminator as the inks are pre-cured and/or cured by the illuminator. The lens allows the UV radiation to pass through the lens while reflecting heat or infrared radiation. Medias that are heat or pressure sensitive are thus protected from excessive heat while permitting the ink to be pre-cured and/or cured.
In another example, the illuminator may include separate light sources. One of the light sources serves to pre-cure the inks while the other light source fully cures the inks. For example, low power mercury, xenon and suntan lamps can be used to pre-cure the inks, while high power lamps can be used to fully cure the inks.
The illuminator is configured to pre-cure the inks before they are fully cured. Pre-curing the UV inks has the advantage of permitting all of the layers to be fully cured in a single layer. As the various colors of ink are placed on the media, they are pre-cured such that they do not merge with other inks. The image quality is thus enhanced and the colors of the various inks are merged by a viewer""s eyes. The inks thus lay next to each other and are fully cured as a thin film. This prevents one ink from obscuring or otherwise interfering with other inks.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The features and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.